As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased. Among them is a lithium secondary battery having high energy density and operating voltage and excellent preservation and service-life characteristics, which has been widely used as an energy source for various electronic products as well as for the mobile devices.
Based on their external and internal structures, secondary batteries are generally classified into a cylindrical battery, a prismatic battery, and a pouch-shaped battery. Especially, the prismatic battery and the pouch-shaped battery, which can be stacked with high integration and have a small width to length ratio, have attracted considerable attention.
Also, the secondary batteries have attracted considerable attention as an energy source for electric vehicles and hybrid electric vehicles, which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel. As a result, kinds of applications using the secondary batteries are being diversified owing to advantages of the secondary batteries, and hereafter the secondary batteries are expected to be applied to more applications and products than now.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery will be heated or explode due to overcharge, overcurrent, or any other external physical impacts. In other words, the lithium secondary battery has low safety. For this reason, a method of mounting elements outside a cell to secure the safety of the battery is under discussion. The elements may include a protection circuit module (PCM) for effectively controlling the abnormality of the lithium secondary battery, such as overcharge, a positive temperature coefficient (PTC) element and a circuit interruption device (CID) element using the change in temperature of the battery, and a safety vent using the change in internal pressure of the battery.
The PCM includes a field effect transistor (FET), which serves as a switching element for controlling electric current conduction, a voltage detector, and passive elements such as a resistor and a capacitor. The PCM interrupts overcharge, overdischarge, overcurrent, short circuits, and reverse voltage of the battery cell to prevent the explosion or the overheating of the battery cell, the leakage of liquid from the battery cell, and the degradation of the charge and discharge characteristics of the battery cell, and to suppress the lowering of the electrical efficiency of the battery cell and the abnormal physicochemical behavior of the battery cell, thereby eliminating dangerous factors from the battery cell and increasing the service life of the battery cell. The PTC element is electrically connected between an electrode assembly of the battery cell and an external input and output terminal such that, at a temperature at which the battery cell normally operates, the PTC element maintains low resistance to allow electric current to flow therethrough, and, in an abnormal state, such as overcurrent or high temperature, of the battery cell, the resistance of the PTC element abruptly increases with the increase of the temperature, whereby the PTC element cuts itself off or only a small amount of current flows through the PTC element. Consequently, The PTC element serves to suppress the increase in internal pressure of the battery due to the overheating of the battery.
In the battery pack including the PTC element, for example, the PCM having the external input and output terminal is connected to a cathode terminal and an anode terminal via conductive nickel plates by welding or soldering, and the PTC element attached to the nickel plates at the top and bottom thereof are electrically connected to the PCM and the electrode terminals of the battery cell.
In order to assemble the battery pack with the above-stated construction, however, several welding or soldering processes are required to achieve the electrical connection between the PTC element and the PCM and between the PTC element and the electrode terminals. Furthermore, since the PTC element is connected to the PCM and the battery cell, it is required for the nickel plates to have a large length. The long nickel plates must be bent such that the PCM is loaded on the battery cell, with the result that a dead space corresponding to the bent space is formed, and therefore, the volume density of the battery pack relatively decreases as compared with other battery packs having the same standard.
For the above-mentioned reason, in a method of mounting elements on a board to manufacture the PCM, there has been developed a technology for manufacturing a very thin PCM using a chip-on-board technology to reduce the overall volume of the battery pack and loading the PCM on the top of the battery pack. However, the PCM manufactured using the chip-on-board technology is higher in price that a PCM manufactured according to the conventional art, with the result that the manufacturing costs of the battery pack increases.
Therefore, research has been actively made on various technologies for efficiently utilizing the space at the upper end of the battery pack in which the PCM is loaded to easily assemble an insulative mounting member and a safety element loaded on the top of the battery cell and, at the same time, not to increase the overall volume of the battery pack even when using a battery pack including the PCM manufactured according to the conventional art.
In connection with this matter, for example, Korean Patent Application Publication No. 2007-0097143 discloses a secondary battery including an electrode assembly constructed in a structure in which two different electrodes are wound while a separator is disposed between the two electrodes, a container in which the electrode assembly is mounted, and a cap assembly coupled to an open top of the container, wherein an insulation case is mounted between the electrode assembly and the cap assembly, and the insulation case is provided with a first groove for receiving at least partially a downward protruding region of the cap assembly.
However, the first groove formed at the insulation case is provided to prevent the bending deformation of the insulation case and to minimize an unnecessary space between the cap assembly and the insulation case. As a result, the first groove does not allow the insulative mounting member and the safety element to be easily assembled or does not give a space sufficient for all the elements of the PCM to be introduced thereinto. Consequently, it is difficult to efficiently utilize the space at the upper end of the battery pack. Also, the safety elements, including the PCM, are connected to the electrode terminals of the battery cell by welding or soldering, with the result that the battery pack assembling process is complicated.
Consequently, there is a high necessity for a technology that is capable of reducing the number of members mounted to the top of the battery cell to simplify the assembling process, achieving the connection between the PCM and the insulative mounting members in a no-welding manner, and mounting the safety elements, such as the relatively thick PCM and the PTC element, to the top of the battery pack while not increasing the thickness of the battery pack.